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EP2008589A1 - Procédé et appareil de formation d'une image avec des données projectives dynamiques - Google Patents

Procédé et appareil de formation d'une image avec des données projectives dynamiques Download PDF

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Publication number
EP2008589A1
EP2008589A1 EP08251981A EP08251981A EP2008589A1 EP 2008589 A1 EP2008589 A1 EP 2008589A1 EP 08251981 A EP08251981 A EP 08251981A EP 08251981 A EP08251981 A EP 08251981A EP 2008589 A1 EP2008589 A1 EP 2008589A1
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Prior art keywords
data
energy
along
space
relative
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German (de)
English (en)
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Mark Doyle
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Allegheny Singer Research Institute
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
    • G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
    • G01R33/561—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution by reduction of the scanning time, i.e. fast acquiring systems, e.g. using echo-planar pulse sequences
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • G01R33/4818—MR characterised by data acquisition along a specific k-space trajectory or by the temporal order of k-space coverage, e.g. centric or segmented coverage of k-space
    • G01R33/4824—MR characterised by data acquisition along a specific k-space trajectory or by the temporal order of k-space coverage, e.g. centric or segmented coverage of k-space using a non-Cartesian trajectory
    • G—PHYSICS
    • G06—COMPUTING OR CALCULATING; COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T11/00—2D [Two Dimensional] image generation
    • G06T11/003—Reconstruction from projections, e.g. tomography
    • G06T11/006—Inverse problem, transformation from projection-space into object-space, e.g. transform methods, back-projection, algebraic methods
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
    • A61B6/02—Arrangements for diagnosis sequentially in different planes; Stereoscopic radiation diagnosis
    • A61B6/03—Computed tomography [CT]
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
    • A61B6/54—Control of apparatus or devices for radiation diagnosis
    • A61B6/541—Control of apparatus or devices for radiation diagnosis involving acquisition triggered by a physiological signal
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
    • G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
    • G01R33/561—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution by reduction of the scanning time, i.e. fast acquiring systems, e.g. using echo-planar pulse sequences
    • G01R33/5619—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution by reduction of the scanning time, i.e. fast acquiring systems, e.g. using echo-planar pulse sequences by temporal sharing of data, e.g. keyhole, block regional interpolation scheme for k-Space [BRISK]
    • G—PHYSICS
    • G06—COMPUTING OR CALCULATING; COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T2211/00—Image generation
    • G06T2211/40—Computed tomography
    • G06T2211/412—Dynamic

Definitions

  • the present invention is related to forming an image with dynamic projective data. More specifically, the present invention is related to forming an image with dynamic projective data where interpolation or filtering is applied circumferentially or temporally based on the density of sampling of k-space.
  • the projective spatial encoding techniques are widely used in medical imaging, including nuclear medicine, computed tomography (CT), and to a lesser extent, in magnetic resonance imaging (MRI).
  • CT computed tomography
  • MRI magnetic resonance imaging
  • images are acquired in a time resolved manner, typically to show motion throughout the cardiac cycle.
  • Each image frame is reconstructed from a series of projective views of the patient, with the series of projective views for that slice at that point in the cardiac cycle taken at a number of equally spaced angular positions around the body.
  • CT and MRI there may be 200-300 projective views per slice per time point in the cardiac cycle, and in lower-resolution nuclear medicine, there are typically 60-100 projective views per slice per time point.
  • VIPRE VIPRE
  • STAR dynamic projective data, but there is no requirement for the data to be stationary.
  • the present invention pertains to an apparatus for forming an image of a body of a patient.
  • the apparatus comprises an energy source which emits energy that passes through the body or which causes the body to emit energy.
  • the apparatus comprises at least one detector element which receives the energy which has passed through, or originated within the body.
  • the apparatus comprises a computer with a memory in communication with the detector element which stores in the memory angular and timing information relative to the body regarding the energy.
  • the apparatus comprises means for obtaining additional angular and timing information relative to the body regarding the information including the computer-generated steps from a computable readable medium of: acquiring time resolved projective data, either in a sparse manner or in a highly sampled manner, depending on which acquisition aspect of the patient is to be reduced; interpolating either along a circumferential direction or along a temporal direction sparsely sampled data, the interpolation direction being determined by a relative k-space sampling density; applying data filtering either along the circumferential direction or along the temporal direction for highly sampled data, the filtering direction being determined by the relative k-space sampling density; compiling a full radial sampling set from the filtered or interpolated data; and submitting the sampling set for reconstruction.
  • the present invention pertains to a method for forming an image of a patient.
  • the method comprises the steps of acquiring time resolved projective data, either in a sparse manner or in a highly sampled manner, depending on which acquisition aspect of the patient is to be reduced.
  • the filtering direction being determined by the relative k-space sampling density.
  • compiling a full radial sampling set from the filtered or interpolated data There is the step of submitting the sampling set for reconstruction.
  • Figure 1A shows the k-space lines arranged in a parallel manner that is typical of an MRI acquisition.
  • Figure 1B corresponds to an acquisition of projective data, where each projection is represented by a separate line passing through the center of k-space.
  • Figure 2 is an illustration of the form of the relative density of k-space coverage for a radial scan and a parallel line scan.
  • Figure 3 is an illustration of how a series of radial lines are acquired over time.
  • Figure 4 shows an application of STAR to a modality such as MD-CT.
  • Figure 5 shows an application of STAR to a modality such as gated-SPECT.
  • Figure 6 shows the low pass filtering of the circumferential data in STAR.
  • Figure 7 shows the low pass filtering of the temporal data in STAR.
  • Figure 8 is a block diagram of STAR.
  • Figure 9 is a block diagram of CT hardware for computed tomography in regard to STAR.
  • Figure 10 is block diagram of gated SPECT hardware in regard to STAR.
  • Figure 11 is a block diagram of MRI hardware in regard to STAR.
  • Figure 12 is a schematic of the k-space sampling pattern for radial lines.
  • Figure 13 is a block diagram of the apparatus of the present invention.
  • an apparatus 10 for forming an image of a body of a patient comprises an energy source 12 which emits energy that passes through the body or which causes the body to emit energy.
  • the apparatus 10 comprises at least one detector element 14 which receives the energy which has passed through, or originated within the body.
  • the apparatus 10 comprises a computer 16 with a memory 18 in communication with the detector element 14 which stores in the memory 18 angular and timing information relative to the body regarding the energy.
  • the apparatus 10 comprises means 20 for obtaining additional angular and timing information relative to the body regarding the information including the computer-generated steps from a computable readable medium of: acquiring time resolved projective data, either in a sparse manner or in a highly sampled manner, depending on which acquisition aspect of the patient is to be reduced; interpolating either along a circumferential direction or along a temporal direction sparsely sampled data, the interpolation direction being determined by a relative k-space sampling density; applying data filtering either along the circumferential direction or along the temporal direction for highly sampled data, the filtering direction being determined by the relative k-space sampling density; compiling a full radial sampling set from the filtered or interpolated data; and submitting the sampling set for reconstruction.
  • the source can be a collimated x-ray source 22.
  • the detector element 14 can include a detector array 24.
  • the obtaining means 20 can include a motor 26 or electrical control which moves the x-ray source 22.
  • the energy source 12 can include a radioactive source 28 which is adapted to be introduced to the body and which emits high-energy photons as a result of radioactive decay.
  • the detector element 14 can include a detector array 24.
  • the obtaining means 20 can include a motor 26 which moves the detector array 24 along a circular or a ellipsoidal trajectory around the body and when a next angular position is reached, a motor 26 stops moving the detector array 24 and the detector array 24 collects new data and position information.
  • the energy source 12 can produce imaging gradients that are applied in a radial manner to obtain k-space data.
  • the detector element 14 includes a detector coil 30 and electronics which converts electrical voltage information into digital values.
  • the obtaining means 20 includes altering the imaging gradients strengths to obtain data and a next angular position.
  • the present invention pertains to a method for forming an image of a patient.
  • the method comprises the steps of acquiring time resolved projective data, either in a sparse manner or in a highly sampled manner, depending on which acquisition aspect of the patient is to be reduced.
  • the filtering direction being determined by the relative k-space sampling density.
  • the step of reconstructing the sampling set to form the image there is preferably the step of emitting energy that passes through the body.
  • the apparatus otherwise known as STAR, describes a rapid acquisition and reconstruction process that is applicable to imaging approaches that acquire projective data in a time-resolved manner.
  • the invention allows fewer projections, e.g. 75% fewer projections, compared to a full scan satisfying the Nyquist sampling criteria.
  • the STAR scan retains spatial and temporal resolution and signal to noise ratio comparable to the fully sampled conventional scan.
  • the principle of the STAR invention is that projective data populate the signal space, k-space, at densities that vary along the radial axis, and that in a time resolved data set, the data at some regions of k-space are more highly sampled spatially, and at other regions of k-space the data are more highly sampled temporally.
  • the processing applied in STAR allows two modes of operation: 1) time resolved projective data are acquired in a sparse manner and the STAR data processing applied to generate projective views that were not directly sampled, 2) time resolved projective data are acquired in a highly resolved manner, and the STAR data processing applied to generate projective views with increased signal to noise ratio.
  • over sampling is defined as the additional number of radial lines that are acquired relative to the parallel line acquisition.
  • the number of lines is doubled compared to a parallel scan, and yields the same Nyquist sampling density at the outermost part of k-space around the circumferential direction axes.
  • Figure 1A shows the k-space lines arranged in a parallel manner that is typical of an MRI acquisition.
  • the lines are typically acquired parallel to one major axis, and are evenly spaced through the matrix.
  • Figure 1B corresponds to an acquisition of projective data, where each projection is represented by a separate line passing through the center of k-space, i.e. radial data.
  • the key feature of the radial plot is that the concentration of k-space lines is highest at the center and gets progressively less towards the periphery of k-space.
  • To satisfy the Nyquist criteria in the radial case requires that there are at least twice as many k-space lines as present in the corresponding parallel case.
  • Figure 2 is an illustration of the form of the relative density of k-space coverage for a radial scan and a parallel line scan.
  • the vertical axis plots the density of k-space sampling, and shows that the data are relatively over sampled by up to a factor of greater than 60 in this case, but that the relative density falls to about 0.5 in the outer regions of k-space, the horizontal axis plots the radius from the center of k-space.
  • the exact shape and amplitude of the relative sampling pattern varies as a function of the over sample factor used for the radial scan, with an over sample value of 2 or higher being typical.
  • Figure 3 is an illustration of how a series of radial lines are acquired over time.
  • the first radial line is re-sampled only after three separate radial lines are sampled. In this manner, each radial line will be sampled at every fourth time point.
  • the central region of k-space corresponds to low-resolution features in the final image that largely contribute to broad contrast features, which typically change in a rapid manner.
  • the outer regions of k-space correspond to fine detail in the final image, but provide very little contrast information, and these regions vary in a relatively slow temporal manner.
  • the exact manner in which the STAR approach can be used to achieve rapid imaging is to some extent coupled to the manner in which radial data are acquired.
  • MD-CT scanning for instance, the scanner detector rapidly rotates around the body and it is more feasible to acquire radial data in a sparse manner (to be illustrated below).
  • the radiation dose (which is typically a limiting factor of MD-CT) can be reduced.
  • gated-SPECT imaging the scanner detector can only move relatively slowly, and radiation dose is not dependent on the scan time. In this case, it is advantageous to apply STAR to increase spatial and temporal resolution (to be illustrated below) since these are typically limiting factors of gated-SPECT data sets.
  • STAR To illustrate the basic principle of STAR that is applicable for modalities such as MD-CT, consider that the conventional radial sampling scheme employs an over-sample factor of 2. Taking this as the reference data set, implement STAR by sampling only every 4th radial lines of k-space at each time point, i.e. the net acquisition time is reduced by a factor of 4. When viewed as a time-radial sampling plot, the sampled points and skipped data are distributed as shown in Fig 4 . In this representation, the position of the sampled points and the skipped points are known for each radial position.
  • the time vs. radial position data are treated separately depending on whether the radial position corresponds to a k-space region that is relatively over-sampled or under-sampled compared to the comparable parallel line scan.
  • k-space is relatively over-sampled for points up to one quarter of the radius from the center, and from the center to this boundary, data are interpolated only along the circumferential direction.
  • Figure 4 shows an application of STAR to a modality such as MD-CT, illustrating the temporal and circumferential distribution of sparsely sampled views at one particular radial position, shown for four concessive time points (1-4).
  • the view shown here for one particular radial position is that radial lines are directed into and out of the plane of the page (like spokes of a bicycle wheel pointing towards the viewer).
  • the vertical axis of the figure represents progression around the circumference, and the horizontal axis represent progression of time.
  • the dark shaded circles represent data that are acquired. Open shaded circles represent positions where radial lines are conventionally acquired but that are not sampled in this particular sparse sample scheme.
  • STAR is arranged for the scanner to dwell at each radial position for a fraction (in this case 50%) of the conventional time (conventionally, the scanner dwells at each position until a certain number of counts are obtained, such as 5,000,000), and to bin the data temporally into double the number of time slots. In this way, high spatial and temporal resolution data will be acquired, but will typically not be of diagnostic value to the excessive noise contamination.
  • Figure 5 shows an application of STAR to a modality such as gated-SPECT illustrating the temporal and circumferential distribution of highly sampled views at one particular radial position, shown for four concessive time points (1-4).
  • the view shown here for one particular radial position is that radial lines are directed into and out of the plane of the page (like spokes of a bicycle wheel pointing towards the viewer).
  • the vertical axis of the figure represents progression around the circumference, and the horizontal axis represent progression of time.
  • the dark shaded circles represent data that would have been conventionally acquired, and the light shaded circles represent the additional radial data that are acquired for STAR.
  • the designation C1 and C2 indicate that conventionally data would be acquired over a temporal duration of twice the duration of that used for STAR in this example. In this case, there are double the number of time points available in the STAR acquisition.
  • the fully resolved gated-SPECT data set When the fully resolved gated-SPECT data set has been acquired it is subjected to data processing using the STAR approach to improve the signal to noise ratio.
  • the boundary of the over sampled region of k-space is identified and within this region (i.e. towards the center of k-space) the fully sampled circumferential data, at each radial position, are filtered along the circumferential direction by applying a low pass filter.
  • the pass width of the filter is determined by the relative density of k-space sampling, e.g. for the case where the sampling density is twice the Nyquist limit, then the band-pass filter would allow through only half of the frequency response data, Fig 6 .
  • the data will be low pass filtered along the temporal direction, Fig 7 .
  • the band-pass width of the low-pass filter is established according to the position along the radial distance from the center of k-space starting with low pass filter width being equal to the full bandwidth at the Nyquist boundary, and progressively reducing towards the periphery of k-space.
  • the lower limit of the band-pass filter could be set to allow through a fraction, such as 1/8 th of the full temporal bandwidth.
  • Figure 6 shows the low pass filtering of the circumferential data in STAR.
  • the original circumferentially sampled points are converted to the frequency domain by performing a Fourier transform.
  • the data are subjected to a low pass filter.
  • the filtered data are converted back to projection data, but with reduced noise.
  • Figure 7 shows the low pass filtering of the temporal data in STAR.
  • the original temporally sampled points are converted to the frequency domain by performing a Fourier transform.
  • the data are subjected to a low pass filter.
  • the filtered data are converted back to projection data, but with reduced noise.
  • FIG. 8 A block diagram of the essential features of STAR is shown in figure 8 .
  • the invention has a dramatic impact on several technologies, including magnetic resonance imaging (MRI), multiple detector computed tomography (MD-CT), and gated radionuclide single photon computed tomography (gated-SPECT) nuclear imaging.
  • MRI magnetic resonance imaging
  • MD-CT multiple detector computed tomography
  • gated-SPECT gated radionuclide single photon computed tomography
  • the hardware that accomplishes CT imaging has several variants with four distinct "generations" of technology are recognized. The variations are largely concerned with whether the detectors move relative to the x-ray source 22, how-many detectors are used, and whether the x-ray source 22 moves around the body in a continuous circle or partial circular path. These variants do not affect the essential features of the STAR invention.
  • the essential features of the CT system are noted in the block diagram and are: an x-ray source 22 that is applied in a pulsed mode to irradiate the body, an array of detectors where the signal is digitized and stored in a memory 18 along with information concerning the relative angle, longitudinal position and timing within the cardiac cycle.
  • a series of projection data sets are obtained in this way that relate to several slices and times within the cardiac cycle. For one cardiac phase time as it relates to an individual slice, the projection data are acquired at a series of angular positions around the body. To obtain increased resolution, an increased number of projections are required, with the variable that increases being the number of projections per
  • the essential features of the gated SPECT system are noted in the block diagram and are: an array of detectors that convert high-energy photons into an electrical signal.
  • the photons are emitted from a radioactive source 28 within the body.
  • the signal from each detector is digitized and stored in a memory 18 along with information concerning the relative angle and timing within the cardiac cycle.
  • a series of projection data sets are obtained by moving the detector array 24 to a new location following an ellipsoidal path around the body. In this way data relating to several slices and times within the cardiac cycle are obtained.
  • an increased number of projections are required, with the variable that increases being the number of projections per unit angle.
  • the essential features of the MRI system are noted in the block diagram and are: a series of gradients are applied to acquired k-space lines in radial manner.
  • the signal from each receiver coil element is digitized and stored in a memory 18 along with information concerning the relative angle and timing within the cardiac cycle.
  • a series of projection data sets are obtained by altering the relative gradient strengths. In this way data relating to several slices and times within the cardiac cycle are obtained.
  • an increased number of projections are required, with the variable that increases being the number of projections per unit angle.
  • the density with which k-space has to be sampled without introducing signal aliasing is governed by the Nyquist sampling criteria.
  • FIG 12 A schematic of the k-space sampling scheme relative to ⁇ K is shown in Fig 12 . Under conditions that the equation relating field of view to ⁇ K is satisfied, the k-space matrix is said to be fully sampled. If the separation AK is less than indicated by the field of view, then k-space is regarded as highly sampled, and under conditions that the separation ⁇ K is greater than indicated by the formula relating it to the field of view, then k-space is said to be sparsely sampled.
  • the projective data are a projection of some energy function through a 2D slice of the patient and consists of a 1D profile.
  • the corresponding Fourier transformed data is also a 1D profile.
  • the data is inserted into the 3D k-space matrix such that the center of the transform data is positioned at the center of k-space (for a given time position along the 3D data set) and that the angle of the transform data corresponds directly to the angle of the original projection data.
  • a series of projective data are arranged to form a k-space data set that is based on a radial distribution spread over time.

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EP08251981A 2007-06-08 2008-06-06 Procédé et appareil de formation d'une image avec des données projectives dynamiques Withdrawn EP2008589A1 (fr)

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JP6112624B2 (ja) 2011-08-02 2017-04-12 ビューズアイキュー インコーポレイテッドＶｉｅｗｓＩＱ Ｉｎｃ． デジタル顕微鏡撮像の装置及び方法
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KR101330638B1 (ko) * 2012-05-10 2013-11-18 고려대학교 산학협력단 자기 공명 영상 생성 방법 및 그에 따른 자기 공명 영상 생성 장치
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CN115631232B (zh) * 2022-11-02 2023-07-25 佛山读图科技有限公司 一种确定双探头探测器径向位置方法

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